stdio/FreeBSD/fseek.c

   1 /*-
   2  * Copyright (c) 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Chris Torek.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 4. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 static char sccsid[] = "@(#)fseek.c     8.3 (Berkeley) 1/2/94";
  35 #endif /* LIBC_SCCS and not lint */
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD: src/lib/libc/stdio/fseek.c,v 1.44 2008/04/17 22:17:54 jhb Exp $");
  38
  39 #include "namespace.h"
  40 #include <sys/types.h>
  41 #include <sys/stat.h>
  42 #include <errno.h>
  43 #include <fcntl.h>
  44 #include <limits.h>
  45 #include <stdio.h>
  46 #include <stdlib.h>
  47 #include "un-namespace.h"
  48 #include "local.h"
  49 #include "libc_private.h"
  50
  51 #define POS_ERR (-(fpos_t)1)
  52
  53 int
  54 fseek(fp, offset, whence)
  55         FILE *fp;
  56         long offset;
  57         int whence;
  58 {
  59         int ret;
  60         int serrno = errno;
  61
  62         /* make sure stdio is set up */
  63         pthread_once(&__sdidinit, __sinit);
  64
  65         FLOCKFILE(fp);
  66         ret = _fseeko(fp, (off_t)offset, whence, 1);
  67         FUNLOCKFILE(fp);
  68         if (ret == 0)
  69                 errno = serrno;
  70         return (ret);
  71 }
  72
  73 int
  74 fseeko(fp, offset, whence)
  75         FILE *fp;
  76         off_t offset;
  77         int whence;
  78 {
  79         int ret;
  80         int serrno = errno;
  81
  82         /* make sure stdio is set up */
  83         pthread_once(&__sdidinit, __sinit);
  84
  85         FLOCKFILE(fp);
  86         ret = _fseeko(fp, offset, whence, 0);
  87         FUNLOCKFILE(fp);
  88         if (ret == 0)
  89                 errno = serrno;
  90         return (ret);
  91 }
  92
  93 /*
  94  * Seek the given file to the given offset.
  95  * `Whence' must be one of the three SEEK_* macros.
  96  */
  97 int
  98 _fseeko(fp, offset, whence, ltest)
  99         FILE *fp;
 100         off_t offset;
 101         int whence;
 102         int ltest;
 103 {
 104         fpos_t (*seekfn)(void *, fpos_t, int);
 105         fpos_t target, curoff, ret;
 106         size_t n;
 107         struct stat st;
 108         int havepos;
 109
 110         /*
 111          * Have to be able to seek.
 112          */
 113         if ((seekfn = fp->_seek) == NULL) {
 114                 errno = ESPIPE;         /* historic practice */
 115                 return (-1);
 116         }
 117
 118         /*
 119          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 120          * After this, whence is either SEEK_SET or SEEK_END.
 121          */
 122         switch (whence) {
 123
 124         case SEEK_CUR:
 125                 /*
 126                  * In order to seek relative to the current stream offset,
 127                  * we have to first find the current stream offset via
 128                  * ftell (see ftell for details).
 129                  */
 130                 if (_ftello(fp, &curoff))
 131                         return (-1);
 132                 if (curoff < 0) {
 133                         /* Unspecified position because of ungetc() at 0 */
 134                         errno = ESPIPE;
 135                         return (-1);
 136                 }
 137                 if (offset > 0 && curoff > OFF_MAX - offset) {
 138                         errno = EOVERFLOW;
 139                         return (-1);
 140                 }
 141                 offset += curoff;
 142                 if (offset < 0) {
 143                         errno = EINVAL;
 144                         return (-1);
 145                 }
 146                 if (ltest && offset > LONG_MAX) {
 147                         errno = EOVERFLOW;
 148                         return (-1);
 149                 }
 150                 whence = SEEK_SET;
 151                 havepos = 1;
 152                 break;
 153
 154         case SEEK_SET:
 155                 if (offset < 0) {
 156                         errno = EINVAL;
 157                         return (-1);
 158                 }
 159         case SEEK_END:
 160                 curoff = 0;             /* XXX just to keep gcc quiet */
 161                 havepos = 0;
 162                 break;
 163
 164         default:
 165                 errno = EINVAL;
 166                 return (-1);
 167         }
 168
 169         /*
 170          * Can only optimise if:
 171          *      reading (and not reading-and-writing);
 172          *      not unbuffered; and
 173          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 174          * We must check __NBF first, because it is possible to have __NBF
 175          * and __SOPT both set.
 176          */
 177         if (fp->_bf._base == NULL)
 178                 __smakebuf(fp);
 179         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 180                 goto dumb;
 181         if ((fp->_flags & __SOPT) == 0) {
 182                 if (seekfn != __sseek ||
 183                     fp->_file < 0 || _fstat(fp->_file, &st) ||
 184                     (st.st_mode & S_IFMT) != S_IFREG) {
 185                         fp->_flags |= __SNPT;
 186                         goto dumb;
 187                 }
 188                 fp->_blksize = st.st_blksize;
 189                 fp->_flags |= __SOPT;
 190         }
 191
 192         /*
 193          * We are reading; we can try to optimise.
 194          * Figure out where we are going and where we are now.
 195          */
 196         if (whence == SEEK_SET)
 197                 target = offset;
 198         else {
 199                 if (_fstat(fp->_file, &st))
 200                         goto dumb;
 201                 if (offset > 0 && st.st_size > OFF_MAX - offset) {
 202                         errno = EOVERFLOW;
 203                         return (-1);
 204                 }
 205                 target = st.st_size + offset;
 206                 if ((off_t)target < 0) {
 207                         errno = EINVAL;
 208                         return (-1);
 209                 }
 210                 if (ltest && (off_t)target > LONG_MAX) {
 211                         errno = EOVERFLOW;
 212                         return (-1);
 213                 }
 214         }
 215
 216         if (!havepos && _ftello(fp, &curoff))
 217                 goto dumb;
 218
 219         /*
 220          * (If the buffer was modified, we have to
 221          * skip this; see fgetln.c.)
 222          */
 223         if (fp->_flags & __SMOD)
 224                 goto abspos;
 225
 226         /*
 227          * Compute the number of bytes in the input buffer (pretending
 228          * that any ungetc() input has been discarded).  Adjust current
 229          * offset backwards by this count so that it represents the
 230          * file offset for the first byte in the current input buffer.
 231          */
 232         if (HASUB(fp)) {
 233                 curoff += fp->_r;       /* kill off ungetc */
 234                 n = fp->_up - fp->_bf._base;
 235                 curoff -= n;
 236                 n += fp->_ur;
 237         } else {
 238                 n = fp->_p - fp->_bf._base;
 239                 curoff -= n;
 240                 n += fp->_r;
 241         }
 242
 243         /*
 244          * If the target offset is within the current buffer,
 245          * simply adjust the pointers, clear EOF, undo ungetc(),
 246          * and return.
 247          */
 248         if (target >= curoff && target < curoff + n) {
 249                 size_t o = target - curoff;
 250
 251                 fp->_p = fp->_bf._base + o;
 252                 fp->_r = n - o;
 253                 if (HASUB(fp))
 254                         FREEUB(fp);
 255                 fp->_flags &= ~__SEOF;
 256                 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 257                 return (0);
 258         }
 259
 260 abspos:
 261         /*
 262          * The place we want to get to is not within the current buffer,
 263          * but we can still be kind to the kernel copyout mechanism.
 264          * By aligning the file offset to a block boundary, we can let
 265          * the kernel use the VM hardware to map pages instead of
 266          * copying bytes laboriously.  Using a block boundary also
 267          * ensures that we only read one block, rather than two.
 268          */
 269         curoff = target & ~(fp->_blksize - 1);
 270         if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
 271                 goto dumb;
 272         fp->_r = 0;
 273         fp->_p = fp->_bf._base;
 274         if (HASUB(fp))
 275                 FREEUB(fp);
 276         n = target - curoff;
 277         if (n) {
 278                 if (__srefill(fp) || fp->_r < n)
 279                         goto dumb;
 280                 fp->_p += n;
 281                 fp->_r -= n;
 282         }
 283         fp->_flags &= ~__SEOF;
 284         memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 285         return (0);
 286
 287         /*
 288          * We get here if we cannot optimise the seek ... just
 289          * do it.  Allow the seek function to change fp->_bf._base.
 290          */
 291 dumb:
 292         if (__sflush(fp) ||
 293             (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
 294                 return (-1);
 295         if (ltest && ret > LONG_MAX) {
 296                 fp->_flags |= __SERR;
 297                 errno = EOVERFLOW;
 298                 return (-1);
 299         }
 300         /* success: clear EOF indicator and discard ungetc() data */
 301         if (HASUB(fp))
 302                 FREEUB(fp);
 303         fp->_p = fp->_bf._base;
 304         fp->_r = 0;
 305         /* fp->_w = 0; */       /* unnecessary (I think...) */
 306         fp->_flags &= ~__SEOF;
 307         memset(&fp->_mbstate, 0, sizeof(mbstate_t));
 308         return (0);
 309 }